In recent years, liquid crystal display devices using a liquid crystal display panel and plasma display devices using a plasma display panel (hereinafter simply referred to as a PDP) have been gaining attention as display devices suitable for achieving a reduction in thickness and an increase in size. These display devices have been produced in large quantities and sales thereof also have been increasing rapidly.
The PDP is composed of a pair of panels, a front panel and a back panel, each having a glass substrate. The front panel includes a front glass substrate on which a display electrode pair, a dielectric layer, a protective layer, etc. are formed. On the other hand, the back panel includes a back glass substrate on which a data electrode, a barrier rib, a phosphor layer, etc. are formed. The front panel and the back panel are disposed facing each other so that a minute discharge space is formed therebetween. A gap between a peripheral portion of the front panel and a peripheral portion of the back panel is sealed with a sealing material. The discharge space is filled with a discharge gas containing neon (Ne), xenon (Xe), etc.
A chassis member is attached to a back surface of the back panel of the PDP via a joining member such as an adhesive heat-conducting sheet and an adhesive agent, etc. A peripheral portion of the chassis member is fixed to a mounting metal piece with screws. The chassis member is a substrate for supporting and fixing the PDP and attaching thereto circuit boards on which a drive circuit for driving the PDP is formed. The chassis member also has a function of radiating effectively the heat generated by the PDP. Furthermore, the plasma display device includes a front frame and a back cover for protecting the PDP and the circuit boards. On a front side of the PDP, a front protective glass substrate is disposed spaced apart from a surface of the front panel of the PDP. The front protective glass substrate is attached to a front housing portion having an opening corresponding to an effective display region of the front panel of the PDP. The front protective glass substrate has functions of color tone correction, contrast improvement, and electromagnetic wave blocking.
In contrast to the back panel fixed by the chassis member, the front panel merely is fixed, at the peripheral portion thereof, only by a sealed portion composed of the sealing material. Therefore, when the plasma display device drops forward (with the front protective glass substrate facing down) during transportation or unpacking, the front panel is warped in the shape of a bowl taking the sealed portion as the supporting point, and has cracks and fractures. More specifically, although the back panel is warped merely in accordance with the warpage of the chassis member, the front panel is warped further from the state of being warped by the warpage of the chassis member. Since the warpage of the chassis member is superimposed on the warpage of the front panel in this way, the front panel tends to be damaged easily.
In order to prevent the cracks in and breakage of the front panel, it can be considered to dispose a frame-shaped elastic member in a gap between the surface of the front panel and the front protective glass substrate along a peripheral portion of the effective display region, as disclosed in JP 2003-131580 A, for example. Such a configuration can suppress to some extent the warpage of the front panel that is a cause of the damage to the front panel.
However, considering the fact that the warpage of the chassis member is superimposed on the warpage of the front panel as described above, it is desired to suppress the warpage of the chassis member rather than to suppress the warpage of the front panel directly, in order to prevent damage to the front panel.
JP 2007-33566 A and JP 2002-108225 A each disclose an example in which a measure is taken against the impact to a PDP. Specifically, JP 2007-33566 A discloses an example in which a plurality of spring structures are provided on a chassis member bonded to a PDP by a joining member, and the spring structures are coupled to a back housing portion by a coupling member (spacer). JP 2002-108225 A discloses an example in which a pole penetrating through a back housing portion stands on a chassis member, the pole is supported by an elastic member provided on the back housing portion, and a spring member is disposed between the back housing portion and a stopper provided at a tip of the pole. However, these examples are intended to absorb the impact transmitted from the back housing portion to the PDP by using the spring structures and the spring member, and are not intended to suppress the warpage of the chassis member.